Method of making a removable bottom for a steelmaking furnace from preformed refractory shapes and resulting product

ABSTRACT

A method of making a removable bottom for a steelmaking furnace from preformed basic refractory shapes, said bottom having tuyeres for injecting gas or other material into a bottom blown steelmaking vessel and the product of the method.

United States Patent 11 1 Hubble et al.

METHOD OF MAKING A REMOVABLE BOTTOM FOR A STEELMAKING FURNACE FROM PREFORMED REFRACTORY SHAPES AND RESULTING PRODUCT Inventors: David H. Hubble, Export; John A.

. Lamont, Delmont, both of Pa.

Assignee: United States Steel Corporation, Pittsburgh, Pa.

Filed: May 25, 1972 Appl. No.: 256,689

[52] US. Cl. 266/35, 266/41 [51] Int. Cl. C2lc 5/48 [58] Field of Search 266/35, 36 P, 43, 41

[56] References Cited UNITED STATES PATENTS 51,401 12/1865 Bessemer 266/35 177,118 5/1876 Harbison 266/35 [111 3,799,526 1451 Mar. 26, 1974 177,,119 5/1876 Hal-bison 266/35 190,890 5/1877 Mildren 266/35 520,631 5/1894 Bull 266/36 P 556,539 3/1896 Haws 266/35 FOREIGN PATENTS OR APPLICATIONS 2,478 9/1871 Great Britain 266/35 320,626 4/1902 France 266/35 561,303 1/1923 France 266/35 905,863 9/1962 Great Britain 2661/35 950,787 10/1956 Germany 266/35 Primary Examiner-Gerald A. Dost Attorney, Agent, or FirmRalph H. Dougherty 57 ABSTRACT A method of making a removable bottom for a steelmaking furnace from preformed basic refractory shapes, said bottom having tuyeres for injecting gas or other material into a bottom blown steelmaking vessel and the product of the method.

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In the bottom-blown oxygen steelmaking process as presently practiced, which is known as the Q-BOP process, a furnace, or vessel, has a removable bottom which contains one or more tuyeres. Oxygen and other gases or particulate matter, such as lime or other flux, is blown through the tuyeres into the vessel. The tuyeres and the surrounding refractory in the removable bottom wear during the production of steel in the vessel. Periodically, bottoms which are worn or have damaged tuyeres must be removed from the vessel and replaced between heats.

Heretofore, the usual method of making a removable bottom or plug for a steelmaking vessel has been to cast a mixture of dolomite and tar into a mold on a removable bottom plate. A cas't plug is of relatively low density, because pressure cannot be applied during forming. Further, a cast plug cannot be prefired to sufficiently high temperatures, such as in the range of 2,000 to 3,200" F, to obtain the good properties inherent with ceramic bonding that are obtained in conventionally fired ceramic products. This is for two reasons, first the size of the plug is too large to be placed in such a furnace and secondly, the plug as cast ordinarily has metal tuyeres protruding through it which would be damaged by suchhigh temperatures.

We have invented a method of making a removable bottom by using preformed refractory shapes of a predetermined configuration. I

It is an object of our invention to provide a method of making removable furnace bottoms requiring no forming or heating equipment at the assembly site.

It is also an object to provide a method of making a furnace bottom having an extremely long operating or useful life.

It is a further object of our invention to provide a method of making a furnace bottom having higher density and greater hot strength than bottoms heretofore available, such as those made by casting of dolomitie material.

It is another object to provide a removable bottom for a bottom-blown steelmaking furnace, which bottom has a high density and high hot strength.

FIG. I is a partly diagrammatic vertical sectional I view of a bottom-blown oxygen steelmaking furnace in which the bottom is made in accordance with our invention.

FIG. 2 is a plan view of the refractory plug in the bottom shown in FIG. 1.

FIG. 3 is a plan view of a modified form of bottom in accordance withv our invention.

FIG. 4 is a section on line lV-IV of FIG. 3.

FIGS is a plan view of another modified form of bottom in accordance with our invention.

FIG. 6 is a section on line Vl-VI of FIG. 5.

FIG. 7 is a plan view of still another modified form of bottom.

FIG. 8 is a section on line VIII-VIII of FIG. 7.

FIG. 9 is a plan view of yet another modified form of bottom.

FIG. 10 is a section on line X-X of FIG. 9.

FIG. 11 isaplan view of another modified form of bottom.

FIG. 12 is a section on line XII-XII of FIG. 11.

FIG. 1 shows a bottom-blown oxygen steelmaking vessel 10 which has a removable lhottom 12. The bottom 12 comprises a bottom plate 14, and one or more generally upstanding tuyeres 16 (FIGS. 1,2) which are surrounded by a refractory plug 18 (FIGS. 1,2) and a retaining ring 19 (FIG. 1), which ring 19 is upstanding from plate 14. The bottom plate 14 is fastened to the furnace 10 by bolts 20 (FIG. 1) in holes 21 (FIGS. 3,4). The sides of the plug 18 do not contact the refractory lining 22 of the vessel, but there is. sufficient clearance between the refractories l8 and 22 to permit insertion of a pitch-bearing monolithic material 24 hereinafter described or the like, which material 24 affords a metaland slag-tight seal.

According to our invention, we form the plug 18 of a plurality of high density, pitch bearing refractory shapes 25,26, 27, and 28 (FIG. 2) having predetermined configurations placed around the tuyeres 16 leaving a minimum of open space around each tuyere 16, as shown in FIG. 2. We construct the plug 18 so that the refractory shapes 25,26,27 and 28 generally form the plug into the frustum of a cone or pyramid or other substantially pyramidal shape. The embodiment of FIGS. 1 and 2 is a six-tuyere plug 18 with the tuyeres 16 in a circular pattern. The central cylinder 29 (FIG. 2) is formed of six identical shapes 25. The shapes- 26,27,28 (FIG. 2) surrounding the central cylinder 29 are solid shapes 26, and shapes 27 and 28 each of which has a hemi-cylindrical trough 30 which trough 30 forms a hole for a tuyere 16 when shapes 27 and 28 are emplaced adjacent each other. The hole is filled around the tuyere 16 with a basic monolithic refractory 24. The outermost refractory shapes 32 are placed within the retaining ring 19 to form a substantially solid plug 18. When all the refractory shapes 25,26,27,28 have been installed, one or more bands 35 (FIG. 1) of steel or other material are placed on the plug 18 to prevent movement of the shapes 25,26,27,28 during subsequent steps and during transportation and installation of the completed plug 18 in the'furnace 10.,These bands 35 are left in place permanently. The configuration of each refractory shape 25,26,27,28 must be such that, after installation of the bottom 12 in the furnace 10 and heating the furnace, the refractory shapes cannot move relatively to each other when the furnace is tilted. I Y

The refractory shapes 25,26,27,l28 of FIGS. 1 and 2 have vertical surfaces. Although these shapes 25,26,27,28 apparently can move relatively to one another when furnace 10 is tilted, preheating of the furnace lining 22 prior to charging the furnace 10 expands the refractory shapes, whereby frictional force develops between them to hold them firmly in position rela' tively to one another when the furnace 10 is tilted. If desired, the shapes 25,26,27,28 can be held in position by mortar between each shape. This, of course, is a more expensive method of making the bottom 12.

The exact configuration of refractory shapes used will depend on the desired arrangement of tuyeres 16 in the bottom 12. FIGS. 3 through 12 illustrate several possible alternative configurations but are not meant to limit our invention. The common features of each of the specific arrangements shown are (1) special preformed pitch-bearing basic refractory shapes, (2) a monolithic pitch-bearing basic material 24 or the like filling the voids 30 around the tuyeres 16, (3) provishapes, tongue and groove shapes, etc. After installation of the bottom 12 in the furnace 10, a basic monolithic material 24 or the like is inserted between the plug 18 and permanent lining 22 to provide tightness as illustrated in FIG. 1.

- FIGS. 3 and 4 illustrate a plug 183 formed of inverted arch bricks. The central shape 40 is a frustum of a cone. The surrounding shapes 41, 42, 43, 44 are tapered so the plug 183 acts as an arch when the furnace is inverted, preventing shape movement. The shapes 41, 42, 43, 44 can be the same length in which case the top of the plug 18 will be flat. Alternatively, the shapes 41, 42, 43, 44 can be longer nearer the periphery as shown in FIG. 4 to form a dished upper surface of the plug 18. A dished surface can be formed by emplacing a monolithic refractory material 24 or the like (not shown in FIG. 4) on bottom plate 14 to form the contour desired for the top of the plug 18 then installing equal length shapes thereon. Since shapes 41, 42, 43,44 are positioned at an angle and tuyeres 16 are substantially vertical, hole 46 is formed through shapes 42 and i 43. Monolithic refractory material 24 is inserted in each hole 46 surrounding each tuyere 16 to form a substantially solid plug 18 The embodiment of FIGS. 5 and is a l-tuyere plug 18 Four different special shapes are used around the tuyeres 16 which are in a straight pattern. The four central shapes 50 are quadrants of a cylinder, each having a longitudinal hole 52 which enables the shape 50 to be installed on the tuyere-containing bottom plate 14 with a tuyere 16 in each hole 52. The ten shapes surrounding the central shapes 50 include four shapes 54 which are solid, four shapes 56 which have offset holes 57 and two shapes 58 which have holes 59 on their centerline. The outer shapes 54, 56, 58 engage retaining ring 19. Basic monolithic material 24 or the like is inserted in each hole 52, 57,59 surrounding each tuyere 16 to form a substantially solid. plug 18 Theplug 18 of FIGS. 7 and 8 contains a large central solid shape 65 which is the frustum of a cone. A number, for example six, of tapered intermediate shapes 66 form a solid'cylinder with shape 65. Tuyeres 16 are arranged in a circular pattern in void 68 between center shapes 66 and tapered outer shape 69 disposed outside the shapes 66. The tapered outer shapes 69 are notched at 70 to engage retaining ring 19. Basic monolithic material 24 or the likeis placed in the void 68 between shapes 66 and 69 to form a solid plug 18'.

The plug 18 of FIGS. 9 and 10 includes a central cylindrical shape 72 surrounded by a number of intermediate shapes 73. Each of the shapes 73 abuts a tapered shape 74. A pair of intermediate shapes 73 and their abutting pair of outer shapes 74, each of which shape has a recessed quarter-cylindrical hole, which holes form a hole 75' for a tuyere 16. The hole 75 is then filled with a basic monolithic material 24 or the like to form a substantially solid plug 18. Band 35 is placed around the plug 18 prior to emplacement in furnace 10.

FIGS. 11 and 12 illustrate a plug 18 formed of interlocking shapes 80,81,82,83. Central cylinder 80 has a groove 84 (FIG. 12). Each surrounding intermediate shape 81 has an inward projection 85 which engages groove 84 in cylinder 80 and a groove 86 in its outer surface to receive a similar projection 87 from a shape 82 in the next course. Outer tapered shapes 83 have inward projections 88 (FIG. 12) which engage a groove 89 in the outer surface of shape 82. Tuyeres 16 extend through suitable holes 90 in shapes 82 and the void therebetween is filled with a basic monolithic material 24 or the like in the same manner as FIG. 5.

Tuyeres may extend through one or more shapes as in FIGS. 5 and 6, they may be positioned between rows of shapes as in FIGS. 7 and 8, at the point of communication of four or more shapes as in FIGS. 9 and 10, at the interface of two bricks as in FIGS. 1 and 2, or any combination thereof. Tuyeres can be perpendicular to the bottom plate or at an angle thereto. Of course, the assembly of the plug becomes more difficult as the angle of inclination of the tuyere increases from normal.

PLUG MATERIAL The preformed pitch-bearing basic refractory shapes shown in FIGS. l-12 may be of the pitch-bonded tempered (baked) or pitch-impregnated types in magnesite or dolomite composition (or combinations thereof).' While the refractory composition is not limited, the following table shows the properties of the preferred materials which should be used to insure service performance superior to prior art plugs:

TABLE Acceptable Property Levels Formed Modulus of Bulk 2000 F Rupture at Density Residual 2700 F, Brick Type Ila/cuv ft. Carbon, psi

Tempered magnesite 185 4 Tempered dolomite l75 4 Burnedimpregnated magnesite 180 2 I0O0 Burned-impregnated dolomite l90- l.5 800 Our tempered refractory shapes (FIGS. 1-12) are made of a mixture of a basic refractory aggregate such as magnesite or dolomite or both, high temperature pitch and fine carbon. Magnesite is defined as magnesium oxide derived from naturally occurring carbonates or hydroxides, or derived synthetically from sea water or brine. Dolomite is defined as a mixture of calcium and magnesium oxides derived from naturally occurring carbonates. Our magnesite has a composition of about to 98 percent MgO (on the pitch free basis) and preferably about 94 to 96 percent MgO. Dolomite has a composition of about 38 to 45 percent MgO, with the balance substantially lime. Both magnesite and dolomite are fired to a temperature of above 3,000 F to drive off gases and to produce a dense stable product. The density of this product is defined by its grain porosity. For our application, the grain porosity (i.e., pore volume) of the magnesite or dolomite must be less than 12 percent of total volume and preferably less than 8 percent. The silica content of the refractory aggregate must be no greater than 3.0 percent. A higher silica content will reduce the melting point of the refractory, increasing the wear rate of the plug. The total R 0 content of the dolomite must be limited to 1 percent maximum. R 0 can be iron oxide, aluminum oxide, chromic oxide or boric oxide or the like. These oxides act as a flux on the dolomite and will cause a breakdown of the refractory, increasing the wear rate. Higher R contents can be tolerated in magnesite because it has a higher MgO content. The magnesite or dolomite must be sized in a manner to obtain the maximum product density, but must all be3 mesh.

Fine carbon such as lampblack, fine coke, or fine graphite is mixed with the basic refractory aggregate and preheated to a temperature of 300 to 600 F. The particle size of the fine carbon must be 100 mesh, and preferably should be -325 mesh. About 85 to 95 parts of magnesite are mixed with 0.5 to 4.0 parts of fine car bon, but we prefer 92 to 94 parts of magnesite and I-Az to 2- /2 parts fine carbon.

Pitch having a ring and ball softening point in the rangefrom 150 to 285 F and preferably in the range of 185 to 230 F is preheated to from 50 to 200 F above its softening point. We mix from 2 to 8 parts of pitch with the previously formed refractory aggregate carbon mixture to form a moldable mass. Preferably about 2 to 6 parts of pitch are employed in the mixture. The pitch should have a Quinoline Insoluble fraction ranging from 8 to 17 percent.

The thoroughly mixed moldable mass is maintained at a temperature of from 50 to 200 F above the softening point of the pitch while it is pressed into a mold to form the desired shape. When pressing is completed, the shape is placed in a muffle oven, baked at a temperature of from 350 to 800 F for a period of from 2 to 100 hours. The preferred baking temperature is from 500 to 600 F, and the preferred baking time is from 6 to 60 hours. In a muffle-type furnace, the pitch volatiles, which are driven off, are retained in the region surrounding the plug to form a reducing atmosphere, thus avoiding oxidation by exposure of the bottom to oxidizing gases.

Our burned-impregnated refractory shapes are of a mixture of a basic refractory aggregate such as magnesite or dolomite, or both, and a high temperature pitch which is subsequently injected into the pores of the brick by vacuum impregnation. The magnesite and do I lomite for the impregnated brick has the same composition, density, sizing and other restrictions as defined above for the tempered brick. This refractory material is pressed with a temporary chemical binder, then fired to a temperature above 2,800 F for at least 30 minutes to form the desired refractory shape. After firing, the shape is placed in a vacuum impregnation chamber and pitch is forced into the pores of the shape. Pitch having a ring and ball softening point from 120 to 250 F, and preferably in the range of 160 to 220 F is used to impregnate the shape.

MONOLITHIC MATERIAL 24 The pitch-bearing basic monolithic material 24 (FIGS. 1-12) to be placed in the space between the preformed shapes and tuyeres may be either a waterbased pitch-bearing material or a mixture of pitch or tar with sized magnesite and dolomite.

Our water-based, pitch-bearing basic refractory monolithic material is made of a mixture of magnesite, high-temperature pitch, fine carbon and a watersoluble chemical bonding agent. Our magnesite has a composition of from 90 to 98 percent MgO and preferably about 94 to 96 percent MgO. The magnesite is fired to a temperature above 3,000 F to drive off gases and to produce a dense stable product. The density of this product is defined by its grain porosity. For our application, the grain porosity (i.e., pore volume) of the magnesite must be less than 12 percent of its total volume and preferably less than 8 percent. The silica con tent of the magnesite must be limited to less than 3 percent. A higher silica content will reduce the melting point of the monolithic refractory material, increasing the. wear rate of the material after installation. The. magnesite must be sized in a manner to obtain the maximum product density, but should all be 3 mesh. We prepare a mixture of:

a. about to percent and preferably 90 to 93 percent magnesite;

b. about 1 to 5 percent and preferably lto 2-% percent fine carbon, such as lamp black, fine coke, or fine graphite;

c. about 2 to 8 percent and preferably 3 to 5 percent ground pitch; and

d. about 1 to 8 percent and preferably 2 to 5 water soluble chemical bonding agent such as chromic acid, sodium silicate, magnesium chloride, magnesium sulfate, or boric acid.

The particle size of the fine carbon and ground pitch must be mesh, and preferably should be 325' mesh to obtain uniform distribution throughout the product.

Any suitable pitch which has a ring and ball softening point in the range of 210 to 300 F and preferably in the high end of the range may be used, including but not limited to petroleum pitch, coal tar pitch and the like. The water soluble chemical binder can be added in dry powder form or premixed with water. The monolithic material may be cast or rammed into the space around the tuyeres in a manner to obtain the best possible density.

Our alternative monolithic material 24 (FIGS. l-l2) is a pitch or tar refractory mixture made of a mixture of magnesite-and/or dolomite, and pitch having a ring and ball softening point from 60 to 250 F. Optionally, fine carbon may be added to this mixture. The magnesite and dolomite requirements are those described above. The mixture comprises 85 to 98 percent refractory aggregate, 2 to 15 percent pitch, and O to 5 percent fine carbon. This mixture may be placed around the tuyeres cold or it may be preheated to liquify the pitch.

The amount of space left around each tuyere shall be the minimum consistent with practical considerations for a particular tuyere arrangement (i.e., from 0 to 3 inches.) Although it is possible for shapes to be so closely fitted around the tuyeres that no monolithic material would be required, size tolerances for the shapes, size of tuyeres, tuyere locations, and other practical considerations make this impossible in nearly all cases. There is no requirement that the tuyere be centered in the space.

As a specific example, we made a plug 18 from burned-impregnated magnesite brick in the general design illustrated in FIGS. 11 and 2. This impregnated magnesite brick had a composition on a pitch-free basis of 95.2 percent MgO, 2.8 percent CaO, 1.3 percent SiO 0.4 percent F6 0,, and 0.3 percent A1 0 The bulk density of the preformed shapes 24,26,27,28 used averaged lbs/cu. ft., the residual carbon content was 2.2 percent, and the modulus of rupture at 2,700 F was 1,250 psi.

These shapes 25,26,27,28 were installed on a bottom plate 14 around the tuyeres l6 and steel bands 35 were applied. A pitch-bearing monolithic material 24 consisting of a mixture of 92 percent magnesite and 8 percent of a 150 F softening point pitch was then rammed into the approximately V2 inch wide space 30 between the tuyeres l6 and surrounding preformed shapes 27,28. The assembled plug 18 was installed in the bottom of a 4()ton experimental Q-BOP vessel 10 which was operated intermittently for 46 heats. The plug 18 had a wear rate of about 0.16 inch per heat.

It is readily apparent from the foregoing that we have invented a method of making a removable bottom for a bottom blown steelmaking process which method requires no forming or heating equipment at the assembly site and which resulting bottom has high density, high hot strength and a longoperating life.

We claim:

1. A removable bottom for a steelmaking furnace comprising:

a metal bottom plate;

a generally upstanding tuyere fixed to said plate;

a plurality of pitch-bearing refractory shapes having a predetermined configuration arranged on said plate and around said tuyere to form a substantially solid plug, with a minimum space about said tuyere, the composition of each of said shapes compr sing;

about 85 to about 95 percent basic refractory aggregate, said aggregate selected from the group comprising magnesite, dolomite and mixtures thereof,

about 9% to about 4 percent fine carbon, and

about 2 to about 8 percent pitch having a ring and ball softening point about 150 to. 285 F,

a pitch-bearing monolithic material in the space between said shapes and said tuyere; and

means for fastening said bottom plate to said furnace.

2. A removable bottom according to claim 1 wherein said'refractory aggregate has asilica content no greater than about 3.0 percent. l

3. A removable bottom according to claim 1 wherein said refractory aggregate has a grain porosity less than about 12 percent of total volume.

4. A removable bottom according to claim 1 wherein said refractory aggregate has a grain porosity less than about 8 percent of total volume.

5. A removable bottom according to claim 1 wherein said shapes consist essentially of tempered magnesite and have a bulk density greater than about 185 lbs per cubic feet and residual carbon content greater than about 4 percent.

6. A removable bottom according to claim 1 in which said refractory aggregate is magnesite having an MgO content of about 85 to about 98 percent.

7. A removable bottom according to claim 6 wherein said shape has a magnesite content of about 92 to about 94 percent.

8. A removable bottom according to claim 1 wherein said shapehas a fine carbon content of about 1-95 to about 2-%.

9. A removable bottom according to claim 1 wherein said fine carbon has a particle size of about -1 00 mesh.

10. A removable bottom according to claim 9 wherein said fine carbon has a particle size of about 325 mesh.

11. A removable bottom according to claim 1 wherein said shape has a pitch content about 2 to about 6 percent.

12. A removable bottom according to claim 1 wherein said pitch has a ring and ball softening point about 185 to about 230 F.

13. A removable bottom according to claim 1 wherein said pitch has a Quinoline Insoluble fraction from about 8 to about 17 percent.

14. A removable bottom according to claim 1 wherein said shape consists essentially of tempered dolomite and has a bulk densitygreaterthan about lbs./cu. ft. and a residual carbon content greater than about 4 percent.

15. A removable bottom according to claim 14 wherein said dolomite comprises about 30 to about 45 percent MgO with the balance substantially lime.

16. A removable bottom according to claim 14 wherein said dolomite has an R 0 content no greater than about 1 percent.

17. A removable bottom according to claim 1 further comprising a retaining ring carried by and upstanding from said bottom plate within which all shapes are positioned.

18. A removable bottom according to claim 1 further comprising a metal band around the periphery of said plug above and substantially parallel to said bottom plate.

19. A removable bottom according to claim 1 wherein said plug is frusto-conical in shape.

20. A removable bottom according to claim 1 wherein said plug is frusto-pyramidal in shape.

21. A removable bottom according to claim 1 wherein said shapes are locked together.

22. A removable bottom according to ,claim 1 wherein adjacent shapes define said space about said tuyere.

23. A removable bottom according to claim 1 wherein said shapes define a flat top surface.

24. A removable bottom according to claim 1 wherein said shapes define an arcuate top surface.

25. A removable bottom according to claim 1 wherein said shapes define a concave top surface.

26. A removable bottom according to claim 1' wherein said shapes define a convex top surface.

27. A removable bottom according to claim 17 wherein the outer portions of said shapes adjacent said retaining ring are provided with a notch to receive said retaining ring.

28. A removable bottom according to claim 1 wherein said space about said tuyere is located in one of said shapes.

29. A removable bottom according to claim 1 wherein said space about said tuyere is on the axis of one of said shapes.

30. A removable bottom according to claim 1 wherein said space about said tuyere is offset from the axis of one of said shapes.

31. A removable bottom according to claim 1 wherein said space about said tuyere is at the point of communication of at least three shapes.

32. A removable bottom according to claim 1 wherein said space about said tuyere is between adjacent courses of shapes.

33. A removable bottom according to claim 1 wherein said shapes are tapered whereby they form an arch preventing movement of said shapes relatively to one another when placed in said furnace.

34. A removable bottom for a steelmaking furnace comprising:

a metal bottom plate;

a generally upstanding tuyere fixed to said plate;

a plurality of pitch-bearing refractory shapes consisting essentially of burned-impregnated magnesite having a bulk density greater than 190 lbs/cu. ft., a residual carbon content greater than about 2 percent and a modulus of rupture at 220 F greater than about 1,000 psi, said shapes having a predetermined configuration and being arranged on said plate and around said tuyere to form a substantially solid plug,'with a minimum space about said tuyere and a pitch-bearing monolithic material in the space between said shapes and said tuyere; and

1 means for fastening said bottom plate to said furnace.

35. A removable bottom according to claim 34 wherein said shape is heated to a temperature about 2,800 F, cooled, then placed in a vacuum chamber and impregnated with pitch having a ring and ball softening point about 120 to about 250 F.

36. A removable bottom according to claim 34 further comprising a retaining ring carried by and upstanding from said bottom plate within which all shapes are positioned.

37. A removable bottom according to claim 34 further comprising a metal band around the periphery of said plug above and substantially parallel to said bottom plate.

38. A removable bottom according to claim 34 wherein said plug is frusto-conical in shape.

39. A removable bottom according to claim 34 wherein adjacent shapes define said space about said tuyere.

40. A removable bottom according to claim 34 wherein said shapes define an arcuate topsurface.

41. A removable bottom according to claim 34 wherein said space about said tuyere is located in one of said shapes.

42. A removable bottom according to claim 34 wherein said space about said tuyere is at the point of communication of at least three shapes.

43. A removable bottom according to claim 34 wherein said space about said tuyere is between adjacent courses of shapes.

44. A removable bottom according to claim 34 wherein said shapes are tapered whereby they form an arch preventing movement of said shapes relatively to one another when placed in said furnace.

45. A removable bottom for a steelmaking furnace comprising:

a metal bottom plate;

a generally upstanding tuyere fixed to said plate;

a plurality of pitch-bearing refractory shapes consisting essentially of burned-impregnated dolomite having a bulk density greater than 190 lbs/cu. ft., a residual carbon content greater than about 1.5 percent and a modulus of rupture at 2,700 F greater than about 800 psi, said shapes having a predetermined configuration and being arranged on said plate and around said tuyere to form a substantially solid plug, with a minimum space about said tuyere and a pitch-bearing monolithic material in the space between said shapes and said tuyere; and

means for fastening said bottom plate to said furnace.

46. A removable bottom according to claim 45 further comprising a retaining ring carried by and upstanding from said bottom plate within which all shapes are positioned.

47. A removable bottom according to claim 45 further comprising a metal band around the periphery of said plug above and substantially parallel to said bottom plate.

48. A removable bottom according to claim 45 wherein said plug is frusto-conical in shape.

49. A removable bottom according to claim 45 wherein adjacent shapes define said space about said tuyere.

50. A removable bottom according to claim 45 wherein said shapes define an arcuate top surface.

51. A removable bottom according to claim 45 wherein said space about said tuyere is located in one of said shapes.

52. A removable bottom according to claim 45 wherein said space about said tuyere is at the point of communication of at least three shapes.

53. A removable bottom according to claim 45 wherein said space about said tuyere is between adjacent courses of shapes.

54. A removable bottom according to claim 45 wherein said shapes are tapered whereby they form an arch preventing movement of said shapes relatively to one another when placed in said furnace.

S5. A removable bottom for a steelmaking furnace comprising:

a metal bottom plate; a generally upstanding tuyere fixed to said plate; a plurality of pitch-bearing refractory shapes having a predetermined configuration arranged on said plate and around said tuyere to form a substantially solid plug with a minimum of space about said tuyere; I

a pitch-bearing monolithic refractory material in the space between said shapes and said tuyere, said pitch-bearing monolithic refractory material comprising;

' a. about to percent magnesite having an MgO content of from about 90 to about 98 per- 7 cerg a g ain porosity less than about 12% of its total volume, and a silica content less than about 7 3 percent;

b. about 1 to about 5 percent fine carbon, having a particle size of about 100 mesh;

c. about 2 to 8 percent solid pitch having a particle size of about 100 mesh and a ring and ball softening point between about 210 to about 300 F, and V (1. about 1 to about 8 percent of a water soluble chemical bonding agentselected from the group consisting of chromic acid, sodium silicate, magnesium chloride, magnesium sulfate and boric acid; and

means for fastening said bottom plate to said furnace.

56. A removable bottom according to claim 55 wherein the magnesite grain porosity is less than about 8 percent.

57. A removable bottom according to claim 55 comprising: wherein the magnesite particle size is about 3 mesh. a metal bottom plate;

' a generally upstanding tuyere fixed to said plate; 58. A removable bottom according to claim 55 a plurality of pitch-bearing refractory shapes having wherein said magnesite has an MgO content of about a predetermined configuration arranged on said 94 to about 96 percent. plate and around said tuyere to form a substantially 59. A removable bottom according to claim 55 solid plug with a minimum of space about said tuwherein said fine carbon is selected from the group yere; consisting of lamp black, fine coke and fine graphite. a pitch-bearing monolithic refractory material in the 1() space between said shapes and said tuyere, said 60. A removable bottom according to claim 55 pitch-bearing monolithic refractory material com wherein said fine carbon has a particle size of about prising; 325 mesh. a. about 85 to about 98 percent basic refractory ag- 61. A removable bottom according to claim 55 gregate having a particle size of about 3 mesh, wherein said pitch has a particle size of about 325 said aggregate selected from the group consisting mesh. of magnesite, dolomite and mixtures thereof,

62. A removable bottomaccording to claim 55 b. about 2 to about 15 percent pitch having a ring wherein the composition of said refractory material is and ball softening point between about 60 to about 90 to about 93 percent magnesite, about 3 to about 250 F, and about 5 percent ground pitch, about I- /z to about 2- /2 c. about 0 to about 5 percent fine carbon, having percent fine carbon and about 2 to about 5 percent a particle size of about -l00 mesh, and water soluble chemical bonding agent. means for fastening said bottom plate to said furnace.

63. A removable bottom for a steelmaking furnace nVntbr(S) It is certified that error appears in the above-identified patent and that said LetterQPate-nt are heareby corrected as shown below:

Column 3; 131116 15, 183* shofild re aci 18 line 16, filggt hbuld read -.1 1; lin 42 916" should read "teen, Column line 46, "at least 36 shsuld refi v--f 'a't' la's't'SO 1601mm 6 iihe 19 after S iH B 4 ZP B '5 line IM shaulid read 2S and e'a ld this 10th day of Septembe r 1974 MCCOY Mo G EBSON JR. c. MARSPALL DANN A'ttesting ilfficer Ccmmissioner of Patents 573m" P5495 a uscoMM-oc 60375-F69 0.5 GOVERNMENT PRINTING OFFICE I 2969 0-.366-334. 

1. A removable bottom for a steelmaking furnace comprising: a metal bottom plate; a generally upstanding tuyere fixed to said plate; a plurality of pitch-bearing refractory shapes having a predetermined configuration arranged on said plate and around said tuyere to form a substantially solid plug, with a minimum space about said tuyere, the composition of each of said shapes comprising; about 85 to about 95 percent basic refractory aggregate, said aggregate selected from the group comprising magnesite, dolomite and mixtures thereof, about 1/2 to about 4 percent fine carbon, and about 2 to about 8 percent pitch having a ring and ball softening point about 150* to 285* F, a pitch-bearing monolithic material in the space between said shapes and said tuyere; and means for fastening said bottom plate to said furnace.
 2. A removable bottom according to claim 1 wHerein said refractory aggregate has a silica content no greater than about 3.0 percent.
 3. A removable bottom according to claim 1 wherein said refractory aggregate has a grain porosity less than about 12 percent of total volume.
 4. A removable bottom according to claim 1 wherein said refractory aggregate has a grain porosity less than about 8 percent of total volume.
 5. A removable bottom according to claim 1 wherein said shapes consist essentially of tempered magnesite and have a bulk density greater than about 185 lbs per cubic feet and residual carbon content greater than about 4 percent.
 6. A removable bottom according to claim 1 in which said refractory aggregate is magnesite having an MgO content of about 85 to about 98 percent.
 7. A removable bottom according to claim 6 wherein said shape has a magnesite content of about 92 to about 94 percent.
 8. A removable bottom according to claim 1 wherein said shape has a fine carbon content of about 1- 1/2 to about 2- 1/2 .
 9. A removable bottom according to claim 1 wherein said fine carbon has a particle size of about -100 mesh.
 10. A removable bottom according to claim 9 wherein said fine carbon has a particle size of about -325 mesh.
 11. A removable bottom according to claim 1 wherein said shape has a pitch content about 2 to about 6 percent.
 12. A removable bottom according to claim 1 wherein said pitch has a ring and ball softening point about 185* to about 230* F.
 13. A removable bottom according to claim 1 wherein said pitch has a Quinoline Insoluble fraction from about 8 to about 17 percent.
 14. A removable bottom according to claim 1 wherein said shape consists essentially of tempered dolomite and has a bulk density greater than about 175 lbs./cu. ft. and a residual carbon content greater than about 4 percent.
 15. A removable bottom according to claim 14 wherein said dolomite comprises about 30 to about 45 percent MgO with the balance substantially lime.
 16. A removable bottom according to claim 14 wherein said dolomite has an R2O3 content no greater than about 1 percent.
 17. A removable bottom according to claim 1 further comprising a retaining ring carried by and upstanding from said bottom plate within which all shapes are positioned.
 18. A removable bottom according to claim 1 further comprising a metal band around the periphery of said plug above and substantially parallel to said bottom plate.
 19. A removable bottom according to claim 1 wherein said plug is frusto-conical in shape.
 20. A removable bottom according to claim 1 wherein said plug is frusto-pyramidal in shape.
 21. A removable bottom according to claim 1 wherein said shapes are locked together.
 22. A removable bottom according to claim 1 wherein adjacent shapes define said space about said tuyere.
 23. A removable bottom according to claim 1 wherein said shapes define a flat top surface.
 24. A removable bottom according to claim 1 wherein said shapes define an arcuate top surface.
 25. A removable bottom according to claim 1 wherein said shapes define a concave top surface.
 26. A removable bottom according to claim 1 wherein said shapes define a convex top surface.
 27. A removable bottom according to claim 17 wherein the outer portions of said shapes adjacent said retaining ring are provided with a notch to receive said retaining ring.
 28. A removable bottom according to claim 1 wherein said space about said tuyere is located in one of said shapes.
 29. A removable bottom according to claim 1 wherein said space about said tuyere is on the axis of one of said shapes.
 30. A removable bottom according to claim 1 wherein said space about said tuyere is offset from the axis of one of said shapes.
 31. A removable bottom according to claim 1 wherein said space about said tuyere is at the point of communication of at least three shapes.
 32. A removable bottom according to claim 1 wherein said space about said tuyere is between adjacent courses of shapes.
 33. A removable bottom according to claim 1 wherein said shapes are tapered whereby they form an arch preventing movement of said shapes relatively to one another when placed in said furnace.
 34. A removable bottom for a steelmaking furnace comprising: a metal bottom plate; a generally upstanding tuyere fixed to said plate; a plurality of pitch-bearing refractory shapes consisting essentially of burned-impregnated magnesite having a bulk density greater than 190 lbs./cu. ft., a residual carbon content greater than about 2 percent and a modulus of rupture at 220* F greater than about 1,000 psi, said shapes having a predetermined configuration and being arranged on said plate and around said tuyere to form a substantially solid plug, with a minimum space about said tuyere and a pitch-bearing monolithic material in the space between said shapes and said tuyere; and means for fastening said bottom plate to said furnace.
 35. A removable bottom according to claim 34 wherein said shape is heated to a temperature about 2,800* F, cooled, then placed in a vacuum chamber and impregnated with pitch having a ring and ball softening point about 120* to about 250* F.
 36. A removable bottom according to claim 34 further comprising a retaining ring carried by and upstanding from said bottom plate within which all shapes are positioned.
 37. A removable bottom according to claim 34 further comprising a metal band around the periphery of said plug above and substantially parallel to said bottom plate.
 38. A removable bottom according to claim 34 wherein said plug is frusto-conical in shape.
 39. A removable bottom according to claim 34 wherein adjacent shapes define said space about said tuyere.
 40. A removable bottom according to claim 34 wherein said shapes define an arcuate top surface.
 41. A removable bottom according to claim 34 wherein said space about said tuyere is located in one of said shapes.
 42. A removable bottom according to claim 34 wherein said space about said tuyere is at the point of communication of at least three shapes.
 43. A removable bottom according to claim 34 wherein said space about said tuyere is between adjacent courses of shapes.
 44. A removable bottom according to claim 34 wherein said shapes are tapered whereby they form an arch preventing movement of said shapes relatively to one another when placed in said furnace.
 45. A removable bottom for a steelmaking furnace comprising: a metal bottom plate; a generally upstanding tuyere fixed to said plate; a plurality of pitch-bearing refractory shapes consisting essentially of burned-impregnated dolomite having a bulk density greater than 190 lbs./cu. ft., a residual carbon content greater than about 1.5 percent and a modulus of rupture at 2,700* F greater than about 800 psi, said shapes having a predetermined configuration and being arranged on said plate and around said tuyere to form a substantially solid plug, with a minimum space about said tuyere and a pitch-bearing monolithic material in the space between said shapes and said tuyere; and means for fastening said bottom plate to said furnace.
 46. A removable bottom according to claim 45 further comprising a retaining ring carried by and upstanding from said bottom plate within which all shapes are positioned.
 47. A removable bottom according to claim 45 further comprising a metal band around the periphery of said plug above and substantially parallel to said bottom plate.
 48. A removable bottom according to claim 45 wherein said plug is frusto-conical in shape.
 49. A removable bottom according to claim 45 wherein adjacent shapes define said space about said tuyere.
 50. A removable bottom according to claim 45 wherein said shapes define an arcuate top surface.
 51. A removable bottom according to claim 45 wherein said space about said tuyere is located in one of said shapes.
 52. A removable bottom according to claim 45 wherein said space about said tuyere is at the point of communication of at least three shapes.
 53. A removable bottom according to claim 45 wherein said space about said tuyere is between adjacent courses of shapes.
 54. A removable bottom according to claim 45 wherein said shapes are tapered whereby they form an arch preventing movement of said shapes relatively to one another when placed in said furnace.
 55. A removable bottom for a steelmaking furnace comprising: a metal bottom plate; a generally upstanding tuyere fixed to said plate; a plurality of pitch-bearing refractory shapes having a predetermined configuration arranged on said plate and around said tuyere to form a substantially solid plug with a minimum of space about said tuyere; a pitch-bearing monolithic refractory material in the space between said shapes and said tuyere, said pitch-bearing monolithic refractory material comprising; a. about 85 to 95 percent magnesite having an MgO content of from about 90 to about 98 percent, a grain porosity less than about 12% of its total volume, and a silica content less than about 3 percent; b. about 1 to about 5 percent fine carbon, having a particle size of about -100 mesh; c. about 2 to 8 percent solid pitch having a particle size of about -100 mesh and a ring and ball softening point between about 210* to about 300* F, and d. about 1 to about 8 percent of a water soluble chemical bonding agent selected from the group consisting of chromic acid, sodium silicate, magnesium chloride, magnesium sulfate and boric acid; and means for fastening said bottom plate to said furnace.
 56. A removable bottom according to claim 55 wherein the magnesite grain porosity is less than about 8 percent.
 57. A removable bottom according to claim 55 wherein the magnesite particle size is about -3 mesh.
 58. A removable bottom according to claim 55 wherein said magnesite has an MgO content of about 94 to about 96 percent.
 59. A removable bottom according to claim 55 wherein said fine carbon is selected from the group consisting of lamp black, fine coke and fine graphite.
 60. A removable bottom according to claim 55 wherein said fine carbon has a particle size of about -325 mesh.
 61. A removable bottom according to claim 55 wherein said pitch has a particle size of about -325 mesh.
 62. A removable bottom according to claim 55 wherein the composition of said refractory material is about 90 to about 93 percent magnesite, about 3 to about 5 percent ground pitch, about 1- 1/2 to about 2- 1/2 percent fine carbon and about 2 to about 5 percent water soluble chemical bonding agent.
 63. A removable bottom for a steelmaking furnace comprising: a metal bottom plate; a generally upstanding tuyere fixed to said plate; a plurality of pitch-bearing refractory shapes having a predetermined configuration arranged on said plate and around said tuyere to form a substantially solid plug with a minimum of space about said tuyere; a pitch-bearing monolithic refractory material in the space between said shapes and said tuyere, said pitch-bearing monolithic refractory material comprising; a. about 85 to about 98 percent basic refractory aggregate having a particle size of about -3 mesh, said aggregate selected from the group consisting of magnesite, dolomite and mixtures thereof, b. about 2 to about 15 percent pitch having a ring and ball softening point between about 60 to about 250* F, and c. about 0 to about 5 percent fine carbon, having a particle size of about -100 mesh, and means for fastening said bottom plate to said furnace. 